1. Field of the Invention
The present invention relates to a method of cleaning and an apparatus for removing organic matters deposited on a semiconductor substrate in a semiconductor device production process.
2. Description of the Related Art
As semiconductor devices are produced in increasingly higher degrees of integration, the devices are required to have increasingly higher reliability. In the process of forming semiconductor elements on a semiconductor substrate that is carried out in a plurality of film forming steps, in particular, cleanliness of the surface of the underlying semiconductor substrate is a critical factor that determines the reliability.
When forming a gate oxide film or a polysilicon film, it is a common practice to keep the semiconductor substrate in a carrier case made of a plastic material for several hours to several days depending on the operating condition of a film forming apparatus.
However, when kept in the carrier case, the semiconductor substrate is often contaminated by organic matters.
When a gate oxide film, for example, is formed on the surface of a semiconductor substrate that is contaminated by organic matters, it is known that the elements formed thereon are prone to problems such as deterioration in the withstanding voltage.
To remove organic matters deposited on the surface of semiconductor, such a method has been employed as irradiating the surface with vacuum ultraviolet light (wavelength: 254 nm) in an ozone atmosphere. This process has sometimes been carried out at a relatively high temperature of 200xc2x0 C. or higher.
However, when irradiating the surface with vacuum ultraviolet light (wavelength: 254 nm) in the ozone atmosphere, there has been a problem that a natural oxide film grows on the substrate before the gate oxide film or polysilicon film is formed thereon. There may also occur such a problem that raising the temperature accelerates the growth of the natural oxide film.
The natural oxide film is not of a good nature, and may affect the reliability of the gate oxide film or the polysilicon film to be formed later.
To solve such problems as described above, it is an object of the present invention to provide a cleaning method of and a cleaning apparatus for removing organic matters deposited on a semiconductor substrate without allowing the natural oxide film to grow on the semiconductor substrate.
The present invention is directed to a method of cleaning a semiconductor substrate, which comprises removing phthalic acid, phthalate or a derivative thereof deposited on the semiconductor substrate by irradiating the semiconductor substrate with vacuum ultraviolet light having a central wavelength of 172 nm.
The wavelength of vacuum ultraviolet light is preferably within a range from 165 to 179 nm. A light source of vacuum ultraviolet light is preferably a Xe excimer lamp.
The present invention is also directed to an apparatus for cleaning a semiconductor substrate, comprising:
an irradiating means disposed in a closed cleaning chamber for irradiating a semiconductor substrate contaminated by phthalic acid, phthalate or a derivative thereof with vacuum ultraviolet light having a central wavelength of 172 nm;
an intake port for introducing oxygen or air into the cleaning chamber;
a semiconductor substrate charging port for charging the semiconductor substrate into the cleaning chamber while shutting off the atmosphere; and
an antechamber of the film forming apparatus through which the semiconductor substrate that has been cleaned in the cleaning chamber is charged into a gate oxide film forming chamber or a polysilicon film forming chamber without being exposed to the atmosphere.
The present invention is further directed to a method of producing a semiconductor device, which comprises effecting a cleaning step as a preliminary step before the step of forming the gate oxide film or the polysilicon film on the semiconductor substrate.
According to the present invention, first, it is made possible to clean the semiconductor substrate that has been kept in a carrier case made of a plastic material and contaminated by phthalic acid, phthalate or a derivative thereof. This is because the irradiation with vacuum ultraviolet light having a wavelength within a range from 165 to 179 nm efficiently generates excited oxygen atoms that decompose the organic matters.
Second, since the cleaning method according to the present invention is effected at a temperature around the room temperature, generation of the natural oxide film can be suppressed.
Third, reliability of the gate oxide film and the polysilicon film can be improved by providing the cleaning step of the present invention immediately before the step of forming the gate oxide film or the polysilicon film.